1. Field of the Invention
The present invention relates to a thermal print head device and a thermal printer including the same, and specifically to the adjustment of pressing force between a thermal print head and a platen roller.
2. Description of the Related Art
In a thermal printer, information is thermally printed on thermal paper using a thermal print head. To achieve high-quality printing, it is important to appropriately bring the paper into close contact with a row of heating elements of the thermal print head. Accordingly, the thermal print head is biased to be pressed against a platen roller which also has the function of feeding the paper. A load (pressing force) by this biasing brings the thermal print head into close contact with the paper passing between the thermal print head and the platen roller.
In some cases, depending on paper to be used, it may be preferred to adjust a biasing force applied to the thermal print head. To satisfy such a demand, there have been proposed techniques (Japanese Patent Application Publication Nos. H7-246752 and H9-216393) to adjust the biasing force acting on the thermal print head using a cam and a technique (Japanese Utility Model Application Publication No. H6-029849) in which the position of a point of action at which the biasing force is exerted on a tiltable header support plate (member supporting the thermal print head) can be moved.
In the techniques (techniques described in Japanese Patent Application Publication Nos. H7-246752 and H9-216393) in which a cam is used to adjust the biasing force applied to the thermal print head, the pressing force applied to the thermal print head is changed according to the profile of the cam. Accordingly, not only a structure for holding the cam but also a mechanism for transferring a change in the profile of the cam to the thermal print head is needed. This results in a complex structure.
On the other hand, in the technique (technique described in Japanese Utility Model Application Publication No. H6-029849) in which the position of a point of action at which the biasing force is exerted on the thermal print head is changed, moment about a fulcrum for tilting is changed by changing the position of the point of action. Because of a configuration in which the whole of a pressing spring which exerts the biasing force is moved, there is the problem that a complex structure is needed to hold the whole of the pressing spring during, before, and after movement.